Flat glass sheets are conventionally heated by a furnace within an insulated housing to a temperature between about 600.degree. and 700.degree. centigrade in preparation for further processing such as bending and tempering or other similar processing. Preheaters have also been previously utilized to provide preheating of glass sheets to a temperature on the order of about 250.degree. to 350.degree. centigrade prior to further heating within an insulated furnace. Such preheaters have previously been of the forced convection type for preheating the glass sheets by hot gas. One problem involved with forced convection preheating of hot glass sheets is providing uniformity of the gas flow that provides the preheating over the entire extent of the flat glass sheet being heated.